Numerical study and modelling of turbulence modulation in a particle laden slab flow

The objective of the present numerical study is the validation of wall-bounded, turbulent particle-laden air flow simulations for a wide range of flow and particle parameters (i.e., flow and particle Reynolds numbers, Stokes number, particle-to-fluid density ratio, ratio of particle diameter to turbulent length scale) covering the one-, two- and four-way coupling regimes. The applied computational fluid dynamics (CFD) model follows the Eulerian two-fluid approach in a Reynolds-Averaged Navier–Stokes (RANS) context and is based on the kinetic theory of granular flow (KTGF) for closures concerning the particulate phase. The fluid turbulence is modeled applying a low-Reynolds-number k–epsilon turbulence model. The main focus is put on the modeling of turbulence coupling between the fluid and the particle phase. Different from common practice, the choice of a model accounting for turbulence modulation is made dependent on the prevailing coupling regime. For the case of four-way coupling, a new modulation model is suggested that well predicts turbulence augmentation and attenuation. The predictive capabilities of the present approach are evaluated by comparing simulation results to experimental benchmark data of various pipe and channel flows. Very good agreement with reference data is obtained for the mean flow and turbulence profiles of both phases.

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Towards an Optimization of Turbulence Effects on Heat and Mass Transfer in Evaporating and Reacting Gas Turbine Sprays

Volume 2: Turbo Expo 2005 ◽

10.1115/gt2005-69038 ◽

2005 ◽

Author(s):

A. Sadiki ◽

M. R. Maneshkarimi ◽

M. Chrigui ◽

J. Janicka

Keyword(s):

Mass Transfer ◽

Gas Turbine ◽

Heat And Mass Transfer ◽

Numerical Study ◽

Combustion Process ◽

Droplet Surface ◽

Mixing Rate ◽

Turbulence Modulation ◽

Swirl Intensity ◽

Turbulence Effects

In this paper, the way towards an optimization of turbulence effects on heat and mass transfer in evaporating and reacting GT-sprays is outlined. It is based on an accurate consideration of coupling between turbulence and turbulence modulation, swirl intensity and non-equilibrium effects during the vaporization. This is achieved by including a physically consistent modelling of turbulence modulation phenomena that allows to better retrieve mass and heat transport effects on the droplet surface, and therefore improves the prediction of processes, like evaporation and combustion, which in turn affect the turbulence. For this purpose, an Euler-Lagrangian method in conjunction with advanced models has been used in RANS-context and applied to the numerical study of a single gas turbine combustor configuration. a) To quantify, to control or to optimize the effects of turbulence along with the swirl intensity effects, a mixing parameter has been introduced. b) Under reacting conditions, it is shown how the evaporation characteristics, mixing rate and combustion process are influenced by turbulence. In particular, the turbulence modulation modifies the evaporation rate, which in turn influences the mixing and the species concentration distribution. It is demonstrated that this effect can not be neglected far from the nozzle for low swirl intensities (Sw.Nu.<1) and close to the nozzle for high swirl number intensities. All these findings can well be used to optimize turbulence effects in evaporating and reacting sprays.

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A numerical study of the modulation of isotropic turbulence by suspended particles

Journal of Fluid Mechanics ◽

10.1017/s0022112098003073 ◽

1999 ◽

Vol 379 ◽

pp. 105-143 ◽

Cited By ~ 165

Author(s):

SHIVSHANKAR SUNDARAM ◽

LANCE R. COLLINS

Keyword(s):

Isotropic Turbulence ◽

Initial Conditions ◽

Numerical Study ◽

Particle Interactions ◽

Initial State ◽

Discrete Energy ◽

Turbulence Modulation ◽

Field Formalism ◽

Particle Velocities ◽

Parameter Values

Direct numerical simulations of a turbulent fluid laden with finite-sized particles are performed. The computations, on a 1283 grid along with a maximum of 262 144 particles, incorporated both direct particle interactions via hard-sphere collisions and particle feedback. The ‘reverse’ coupling is accomplished in a manner ensuring correct discrete energy conservation (Sundaram & Collins 1996). A novel two-field formalism (Sundaram & Collins 1994a) is employed to calculate two-point correlations and equivalent spectral densities. An important consideration in these simulations is the initial state of fluid and particles. That is, the initial conditions must be chosen so as to allow a meaningful comparison of the different runs. Using such a carefully initialized set of runs, particle inertia was observed to increase both the viscous and drag dissipations; however, simultaneously, it also caused particle velocities to correlate for longer distances. The combination of effects suggests a mechanism for turbulence enhancement or suppression that depends on the parameter values. Like previous investigators, ‘pivoting’ or crossover of the fluid energy spectra was observed. A possible new scaling for this phenomenon is suggested. Furthermore, investigations of the influence of particle mass and number densities on turbulence modulation are also carried out.

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